Even as Muscovites choked under a blanket of thick smoke in the first week of August 2010, concentrations of a colorless, odorless gas spiked to dangerous levels. A product of fire and a component of smoke, carbon monoxide is among the pollutants that wildfires spread across much of western Russia. This image, made with data from the Measurements of Pollution in the Troposphere (MOPITT) sensor flying on NASA’s Terra satellite, shows carbon monoxide over western Russia between August 1 and August 8, 2010.

The highest levels of carbon monoxide are shown in red, while lower levels are yellow and orange. Western Russia, including Moscow, sits under a broad area of elevated carbon monoxide. Areas where the sensor did not collect data during the period—probably because of clouds—are gray.

MOPITT measures carbon monoxide in the atmosphere between two and eight kilometers above Earth’s surface. The image shows the composite of those measurements, not carbon monoxide levels near the ground. However, ground measurements of carbon monoxide during the period reached more than six times higher than acceptable levels in Moscow, said news reports.

Carbon monoxide is a dangerous product of fire. The gas can remain in the atmosphere for weeks after being emitted and can therefore travel long distances from the fire that produced it. When it is near the ground where people can breathe it, carbon monoxide poses a health risk. Carbon monoxide binds to red blood cells more easily than oxygen, so it limits the amount of oxygen blood carries through the body. This causes a range of problems from headaches, nausea, and dizziness to cardiovascular problems and confusion. Carbon monoxide is also an ingredient in the production of ground-level ozone, which causes a number of respiratory problems.

NASA Earth Observatory image created by Jesse Allen, using data provided by Gabriele Pfister, the National Center for Atmospheric Research (NCAR) and the University of Toronto MOPITT Teams. Caption by Holli Riebeek.